The invention relates to new isolated immunoglobulins which are devoid of light polypeptide chains. These immunoglobulins do not consist in the degradation products of immunoglobulins composed of both heavy polypeptide and light polypeptide chains but to the contrary, the invention defines a new member of the family of the immunoglobulins, especially a new type of molecules capable of being involved in the immune recognition. Such immunoglobulins can be used for several purposes, especially for diagnosis or therapeutical purposes including protection against pathological agents or regulation of the expression or activity of proteins.
Up to now the structure proposed for immunoglobulins consists of a four-chain model referring to the presence of two identical light polypeptide chains (light chains) and two identical heavy polypeptide chains (heavy chains) linked together by disulfide bonds to form a y- or T-shaped macromolecules. These chains are composed of a constant region and a variable region, the constant region being subdivided in several domains. The two heavy polypeptide chains are usually linked by disulphide bounds in a so-called “hinge region” situated between the first and second domains of the constant region.
Among the proteins forming the class of the immunoglobulins, most of them are antibodies and accordingly present an antigen binding site or several antigen binding sites.
According to the four-chain model, the antigen binding site of an antibody is located in the variable domains of each of the heavy and light chains, and requires the association of the heavy and the light chains variable domains.
For the definition of these four-chain model immunoglobulins, reference is made to Roitt. I et al (Immunology—second-Edition Gower Medical Publishing USA, 1989). Reference is especially made to the part concerning the definition of the four-chain immunoglobulins, their polypeptidic and genetic structures, the definition of their variable and constant regions and the obtention of the fragments produced by enzymatic degradation according to well known techniques.